Membranes formed by self-assembling of amphipathic (amphiphilic) diacetylene molecules exhibit a blue color when polymerized with UV (ultraviolet) irradiation, and such polydiacetylene membranes are known to undergo a change in color to red by the effects of pH, temperature increase, mechanical stress, etc. (see for example, Lipowsky, R. (1991) Nature 349, 475-481; Bloor, D. and Chance, R. R. (1985) Polydiacetylenes: NATO ASI Series E, Applied Science).
Recently, applications of polydiacetylene membranes as biosensors utilizing this property have been proposed (Charych, D. H. et al., (1993) Science 261, 585-588; Reichert, A. et al., (1995) J. Am. Chem. Soc. 115, 1146-1147 (1995); Charych D. H. et al., (1996) Chemistry & Biology 3, 113-120 (1996)). In particular, attempts have been made to construct biosensors in such a manner that the receptors which react specifically with pathogenic bacteria, viruses, toxins and the like present in biosamples are incorporated into polydiacetylene membranes, and the color change (blue to red) induced when the receptors bind to their specific ligands (pathogenic bacteria, viruses, toxins, etc.) is utilized to allow detection of the ligands with high sensitivity. To date, only saccharides and lipids have been used as the receptors in such proposed methods.
Such methods, however, can only be applied to the detection of ligands wherein the binding structure of the receptor and ligand is known and the receptor has been identified. Therefore a number of receptors must be synthesized which is equivalent to the number of types of ligands to be detected, presenting the likely insurmountable difficulty that the conditions for preparation of the polydiacetylene membrane must be determined for the respective cases. Many receptors consisting of saccharides and lipids are highly complicated and difficult to synthesize, while the color change for detection of the ligand is often insufficient. In the method of Charych, et. al. (Chemistry & Biology 3, 113-119 (1996)), for example, gangliosides are incorporated as the receptors for detection of the influenza virus. Because of insufficient color change of the polydiacetylene membrane upon binding between the polydiacetylene membrane and the influenza virus, however, it is necessary to introduce sialic acid into the polydiacetylene at a few percent as a structural change promoter. This complicates the process for preparation of the membrane as a sensor. When the ligands to be detected are different, other types of substances for promoting the structural change must be designed.
In addition, the conventional methods are generally only effective for ligands for which the receptors have molecular weight of about 1000 or less, and the methods are not suitable for detecting ligands which bind to macromolecular receptors. This is because the macromolecular receptors cause color changes in polydiacetylene membranes by simply being incorporated therein.